Driving/Maintenance/Blind spots

The blue car's driver sees the green car through his mirrors but cannot see the red car without turning to check his blind spot.

Blind spots are the areas of the car that cannot be seen while looking forward or through either the rear-view or side mirrors. Blind spots can be eliminated by careful adjustment of side and rear-view mirrors or by adding another mirror with a larger field of view.

Blind spots, as the name suggests, completely hide any object completely positioned within them from the driver's normal field of vision. While looking forward, a driver can check his side and rear areas via mirrors and peripheral vision; any area outside the scope of the mirrors becomes effectively invisible to the driver without dangerously distracting actions such as turning the head to check them.

Because blind spots hide objects, the driver must divert his vision from the road to verify them before making such maneuvers as turns and lane changes. This places the driver in a risky situation: unchecked forward road hazards, such as pedestrians rushing out from behind a parked car, can present themselves in the fraction of time devoted to checking the blind spot; pedestrians, animals, parked cars pulling out without properly checking the road, and other hazards quickly result in collisions. In the case of a parked car pulling out improperly, the force can skew the vehicle's path into the next lane, causing a larger accident or a head-on collision with other traffic.

A large enough blind spot can completely hide a small pedestrian, small motorcycle, or even a full vehicle. Larger vehicles, raised vehicles, and different shaped vehicles such as hatch backs and SUVs have larger blind spots; while a small Sedan may hide little more than a compact motorcycle in its blind spot, a large SUV can hide an entire mid-sized Sedan, and a tractor-trailer can lose entire groups of vehicles behind it and near the right side. Tractors are so high up that any normal sized vehicle immediately to the right sits well below the driver's field of vision. Because of this, you must be aware of both the contents of your own blind spots and other vehicles' blind spots, and stay out of them.

Because blind spots present such a large road hazard, you must remain completely aware of yours and others' blind spots, and deal with them properly. In many cases, your own blind spots can be effectively eliminated by reducing them to such a size that nothing likely to be there while moving will fit in them. In the case of other vehicles, you must be wary of where you sit with the vehicle, and validate that the driver can indeed see you.

You can effectively eliminate your own blind spots by adjusting your mirrors such that a small vehicle or motorcycle doesn't completely fit in the blind spot; that is, before the rear of the vehicle disappears into your blind spot, the front should become visible elsewhere. As the vehicle leaves view of your side mirrors, it should come into your direct peripheral vision. In this way, although you still have a substantial blind spot, you remain completely aware of anything currently in it, regardless of whether you were paying attention when it entered your blind spot or not.

Mirrors adjusted to eliminate blind spots. Notice that the cars don't fit in the blind spots; and peripheral vision or a quick glance to the left will reveal smaller things like motorcycles without a full check over the shoulder.

At the very least, and possibly most effective, a driver can and should adjust his mirrors to eliminate any blind spots around his car. One study[1] found a disturbing trend for side-view mirrors, with 84% of them showing part of the vehicle's side in the left mirror, with the vehicle taking up an average of 21% of the mirror's viewing area. Similarly, 78% of drivers placed their vehicle's side in the right mirror. The average horizontal viewing angles were 12.9 for the left, 25.3 for the rear-view, and 22.5 for the right; for comparison, the diagrams to the right use 15, 30, and 30.

To properly adjust the side- and rear-view mirrors, a driver should make sure the viewing angles don't overlap. There should be enough of a gap that a smaller blind spot is formed, much too small to squeeze a vehicle into; when a vehicle exits the viewing area of the rear-view mirror, it will then inevitably enter the viewing area of a side-view mirror. In this way, all objects in a driver's blind spots will be partially visible in some area visible to the driver, and thus known rather than hidden.

Lean to the left, towards the driver's side window. From this position, adjust the mirror to just barely show the side of the car.

Lean to the right, centering your head inside the vehicle. From this position, adjust the right mirror such that you can again just barely see the side of the car.

Verify visibility when in comfortable driving position. Also verify the vertical alignment of your mirrors; you want to watch down the road, not at the street or sky.

Once the driver has set up his mirrors, he must make sure they don't create large blind spots near the rear corners or passenger doors. If a small motorcycle or bicycle rider can't hide there, then a small car certainly can't. Bicycle riders, by the way, provide a huge pedestrian hazard on city roads; they can pace 30mph with your vehicle, and hide in a wide enough blind spot, so that area definitely needs a small enough blind spot to expose cyclists!

It may take some time for a driver to get used to not having a proper frame of reference with their car. The mirror no longer contains the vehicle, and thus objects in the mirror seem disconnected and abstract; eventually, though, the spatial reference will become inherent to the driver, and driving will become much easier and safer.

A mirror with a wider field-of-view allows for more of the road to show in the mirrors, greatly increasing the visual information available from your mirrors. This allows for greater blind spot elimination using the techniques above, since your mirrors can see more and possibly even overlap.

So-called "blind spot mirrors" add a high-distortion, very wide field-of-view mirror to the corner of your normal mirror. These come in many shapes and sizes, some even with separate ball joint adjustment; they all perform in different manners, too. Some simply cover the same viewing center as your mirror, but much wider, giving a wide-view picture-in-picture; others give a hugely magnified view of your blind spot, basically showing just a vehicle with no context when something's there. In any case, they do remove some normal viewing area from the side mirrors, with the exception of a few models that stack a wide-view mirror on top of your existing mirror assembly.

In general, blind spot mirrors take time to get used to. A driver must train himself to understand what the blind spot mirror relays, and how it fits into the geometry of the vehicle. Oftentimes a quick glance at a blind spot mirror provides a discontinuous, confusing piece of visual information to an untrained driver; of course, given the complex decision making and the wealth of other readily available information, said driver will simply ignore the additional information. Until properly trained to use it, the blind spot mirror provides no advantage, and slight disadvantage due to reduced area of side view mirrors.